As you would expect, the feature is completely opt-in, so the first time you install an app that is not from Google Play, your Android 4.2 running device will ask you if you want such application to be checked for “harmful behavior.”

You can always go to settings and turn this feature on or off. The feature also allows you to check all the installed apps at once for any malicious code.

“We have a catalog of 700,000 applications in the Play Store, and beyond that, we’re always scanning stuff on the Web in terms of APKs that are appearing,” Lockheimer added. “We have a pretty good understanding of the app ecosystem now, whether something’s in the Play Store or not.”

So, if the new security system finds that the app you are installing is not safe, it will alert you and let you decide what you want to do it.

As most of the process of checking the app is done server side, the process is fast and safe.

Google is also introducing a new app permissions screen in Android 4.2, which was far easier to read and understand. Apart from all this, there is another nifty new feature, which will let you know if any app is trying to send an SMS that will cost you